This invention relates to locating metallic objects in an inhomogeneous structure. More particularly, this invention relates to a system and method for accurately determining the depths of reinforcing bars of a reinforced concrete structure such as, for example, a bridge deck, using electromagnetic signals.
A bridge deck is the portion of a bridge upon which vehicles travel. Bridge decks are typically made of reinforced concrete. As referred to herein, concrete is a mixture of fine and coarse aggregates such as, for example, crushed stone or gravel, firmly bound into a monolithic mass by a cementing agent such as, for example, Portland cement. Reinforced concrete as referred to herein is concrete in which metal rods or bars, preferably made of steel, are incorporated into the concrete in such a manner as to reinforce or strengthen the more or less brittle nature of concrete and the resulting structure. Such rods or bars carry the tension to which a concrete structure may be subjected, thus reinforcing the concrete, and are referred to herein as reinforcing bars or rebars. As used herein, a substantially concrete structure is a structure where the primary constituent is concrete. Such a substantially concrete structure may contain reinforcing bars to improve tensile strength, a waterproofing membrane to protect the structure from moisture, an asphalt layer or overlay, other added elements to improve durability or performance, and possible inadvertently added elements.
The depth of the rebars relative to the concrete surface, commonly called xe2x80x9cconcrete cover,xe2x80x9d is important for at least two reasons. First, the depth of the rebar affects the overall tensile strength of the bridge deck, and second, rebar corrosion potential is related to the depth of the rebar in the concrete. Rebar corrosion may compromise the structural integrity of a reinforced concrete bridge deck, and lead to further deterioration of the concrete that further compromises structural integrity. Further, a bridge deck may be subjected to extreme climates such as, for example, snow, ice, and thermal freeze-thaw cycles. Further, such extreme climates, and human intervention to permit the flow of traffic on the bridge amidst these harsh conditions, may result in the ingress of road salt. These factors may lead to the eventual deterioration of portions of the bridge deck, making travel on the bridge unsafe.
Consequently, the State of New Hampshire, USA, has implemented a quality control (QC) policy which rewards bridge contractors who place the rebars at the correct depth in new bridge decks, and penalizes contractors negligent in rebar placement. The QC policy specifies the measurement of rebar cover to within xc2x13 millimeters. The policy also requires the measurement of many rebars per bridge deck, to establish a statistical basis for assessing contractor performance. The large number of rebars that need to be located makes prohibitive the use of invasive techniques, such as, for example, core drilling, to obtain the depths of all of the rebars.
Thus, there is an established need to accurately determine the depth of rebars used in the construction of reinforced concrete bridge decks.
Ground penetrating radar (GPR) is a technique that may be used to image the inside of a structure by collecting the echoes (or reflections) resulting from electromagnetic signals such as, for example, electromagnetic waves of typically high frequency, being radiated into the structure. Typically, the rebars inside a reinforced concrete structure are strong radar wave reflectors. Locating rebars within a reinforced concrete structure and determining their depths may be accomplished by analyzing the reflections, particularly the amplitudes and arrival times of the reflections, from the rebars in the reinforced concrete structure.
In an embodiment, provided is a method of determining, for a substantially concrete structure having at least a first side and containing one or more reinforcing bars, a distance of the one or more reinforcing bars from the first side of the substantially concrete structure. One or more computer-readable data signals are received, and each data signal represents an electromagnetic signal detected from an area of the concrete structure. One or more of the detected electromagnetic signals include electromagnetic energy reflected from the concrete structure as a result of an electromagnetic signal transmitted into the concrete structure. A distance of one or more of the reinforcing bars from the first side of the substantially concrete structure is determined from the one or more computer-readable data signals.
In another embodiment, for a substantially concrete structure having at least a first side and containing one or more reinforcing bars, a system for determining a distance of the one or more reinforcing bars from the first side of the substantially concrete structure is provided. The system includes means for receiving one or more computer-readable data signals, wherein each data signal represents an electromagnetic signal detected from an area within the concrete structure, and wherein one or more of the detected electromagnetic signals include electromagnetic energy reflected from the concrete structure as a result of an electromagnetic signal transmitted into the concrete structure. The system further includes means for determining from the one or more computer-readable data signals a distance of one or more of the reinforcing bars from the first side of the substantially concrete structure.
In an aspect of this embodiment, the means for determining includes means for selecting one or more of the data signals, each selected data signal corresponding to a reinforcing bar, and means for determining, for each selected signal, a first distance of the corresponding reinforcing bar from the first side of the substantially concrete structure.
In another aspect of this embodiment, each data signal represents an electromagnetic signal detected over a detection period of time, and the means for determining the first distance for each selected signal includes means for determining, for each selected signal, a portion of the selected signal during which the electromagnetic signal represents electromagnetic energy reflected from a corresponding reinforcing bar. The means for determining the first distance further includes means for determining, for each data signal, the first distance of the corresponding reinforcing bar from the first side from the determined portion of the selected signal.
In another aspect of this embodiment, the system further comprises means for determining a velocity value representing a velocity of each electromagnetic signal in concrete of the substantially concrete structure. The means for determining the first distance includes means for determining, for each selected signal, a first point in time during the detection period corresponding to a peak amplitude of the selected signal and means for calculating, for each selected signal, the first distance using the velocity value and the first point in time.
In yet another aspect of this embodiment, for each selected signal, the means for determining the first distance further includes means for determining a second point in time corresponding to a peak amplitude of electromagnetic energy reflected from the first side of the substantially concrete structure, means for subtracting the first point in time from the second point in time to produce a propagation time within the concrete structure by the detected signal and means for calculating the first distance using the velocity value and the propagation time.
In yet another aspect of this embodiment, the transmitted signals were transmitted from a first antenna and the detected signals were detected by a second antenna located a second distance from the first antenna. For each selected signal, the means for calculating the first distance includes means for applying an equation:       d    =                  1        2            ⁢                                                  v              2                        ⁢                          t              2                                -                      a            2                                ,
wherein d is the first distance, t is the propagation time, v is the velocity value, and a is the second distance.
In another aspect of this embodiment, the means for determining the first distance includes means for receiving a second distance value indicative of a distance measured from the first side of the concrete structure to one of the one or more reinforcing bars and means for calculating the velocity value from the second distance value.
In another aspect of this embodiment, the transmitted signals were transmitted from a first antenna and the detected signals were detected by a second antenna located a third distance from the first antenna. For each selected signal, the means for determining the first distance includes means for determining a propagation time of the detected signal in the substantially concrete structure, and wherein the means for calculating the velocity value includes means for applying an equation:       v    =                  2        t            ⁢                                                  (                              a                /                2                            )                        2                    +                      d            2                                ,
wherein v is the velocity value, a is the third distance, t is the propagation time and d is the second distance.
In yet another aspect of this embodiment, each transmitted electromagnetic signal was transmitted at a different position along the first side of the concrete structure, and the means for determining the first distance for each selected signal further includes means for determining, for each data signal, a peak amplitude of the data signal during the determined portion. The means for selecting a data signal includes, for one or more spatial intervals of a first length along the first side of the substantially concrete structure, means for selecting a data signal with a peak amplitude of a highest magnitude from among data signals corresponding to electromagnetic signals transmitted within the spatial interval.
In another aspect of this embodiment, the system further comprises means for migrating the data signals to facilitate selecting the data signal with a peak amplitude of the highest magnitude.
In another aspect of this embodiment, the transmitted signals were transmitted from a first antenna and the detected signals were detected by a second antenna located a second distance from the first antenna, the second distance having a midpoint on an imaginary straight between the first and second antennas, and an amplitude of each data signal is directly related to a distance between the area corresponding to the data signal and the midpoint of the second distance.
In yet another aspect of this embodiment, each of the data signals represent an electromagnetic signal detected at a point along a substantially straight line along a first dimension of the first side of the concrete structure, and each detected electromagnetic signal is detected over a period of time. The system further comprises means for displaying a graph of one or more of the data signals, a first axis of the graph representing time of detection, a second axis of the graph representing a distance along the first dimension, the means for displaying including means for representing an amplitude of each of the one or more data signals over the detection time, the location, with respect to the second axis, of each represented data signal corresponding to the point at which the signal was detected.
In another aspect of this embodiment, the means for selecting the data signals includes means for selecting each data signal from the graph in accordance with the amplitudes of the represented data signals.
In another aspect of this embodiment, the means for determining includes means for adjusting the data signals by removing from each data signal data representing electromagnetic signals not reflected from the substantially concrete structure, and means for determining the depth of one or more reinforcing bars of the substantially concrete structure from the adjusted data.
In another embodiment, for a substantially concrete structure having at least a first side and containing one or more reinforcing bars, a system for determining a distance of the one or more reinforcing bars from the first side of the substantially concrete structure is provided. The system includes a computer-readable storage mediun to store one or more computer-readable data signals, wherein each data signal represents an electromagnetic signal detected from the concrete structure, and one or more of the detected electromagnetic signals include electromagnetic energy reflected from the concrete structure as a result of an electromagnetic signal transmitted into the concrete structure, and wherein each detected signal corresponds to an area within the concrete structure. The system also includes a data analysis application 300 to receive the computer-readable data signals and determine from the data signals a distance of one or more of the reinforcing bars from the first side of the substantially concrete structure.
These and other features and advantages of the invention will be more readily understood and appreciated from the detailed description below, which should be read together with the accompanying drawing figures.